This invention relates to an optical-electronic integrated circuit device in which plural optical-electronic integrated circuit substrates, each provided with an electronic circuit, a light emitting element and a light receiving element, are optically coupled in a direction parallel to the substrates. More particularly, it relates to an optical electronic integrated circuit device in which the substrates are stacked three-dimensionally in a direction perpendicular to the substrates for improving the integration degree of the circuit device.
The present tendency is towards a higher integration and a higher operating speed of LSIs (Large Scale Integrated circuits) and ICs employing semiconductors, such as silicon, and compound semiconductors, such as GaAs. In a system such as a work station or a personal computer employing such electronic devices, a demand for a smaller size and a higher operating speed will become more acute in the future,
In LSIs employing the current semiconductor integrated circuits, the interconnection between micro-sized devices formed on a circuit chip is a patterned electrical interconnection of a metal or like material. However, as long as such an electrical interconnection is employed, the problem of delay in transmission is raised when operating at an ultra-high operating speed if an extremely fine pattern of interconnection is used, while the problem of induction noise or mutual interference is raised if the space between interconnections is reduced as the result of increasing the packaging density.
Meanwhile, such problem resulting from ultra high speed or from high density is not present in an optical integrated circuit in which signals are transmitted by light. That is, ultra high operating speeds may be easily achieved in optical-electronic integrated circuits since stray capacitance or inductances between the interconnections are reduced. For time multiplexed transmission, lower power consumption may also be achieved by employing the optical-electronic integrated circuit. For this reason, attention has been directed to transmission of signals between electronic devices by light coupling without relying upon electrical interconnection.
As an example of an apparatus for two-dimensionally accomplishing such light coupling, there is disclosed in JP Patent KOKAI Publication No. 61-121014 (1986) an apparatus which a light interconnecting plate 515 consisting of e.g. an SiO.sub.2 substrate is mounted on a substrate 511 on which a light receiving element Pd and a light emitting element Em are formed, and in which a vee-shaped groove 516 and a high refractive index light guide channel 517 formed by proton radiation on the substrate, as shown in FIG. 1 . The light emitted from the light emitting element reaches a lateral surface of the vee-shaped groove provided in the light interconnection plate. Since the upper part of the light interconnecting plate is covered with a low refractive index substance, such as air, the light may undergo total reflection on the lateral surface of the vee-shaped groove and thence is guided to the light wave guide channel by setting the angle of the lateral surface of the vee-shaped groove to a value not more than the critical angle determined by the refractive index of SiO.sub.2 with respect to air. The light incident on the light wave guide channel is transmitted through the light wave guide channel toward another vee-shaped groove to wherein undergoes total reflection at the lateral surface of the vee-shaped groove to reach the light-receiving element.
However, with the above-described two-dimensional light coupling, the operating speed and the packaging density of the circuit cannot be raised beyond certain limit values. An effective measure for realizing both high operating speed and high density packaging is by three-dimensional integration which provides for integrating the optical-electronic integrated circuit board in a direction perpendicular to the major surface of the circuit board.
However, for signal transmission by light between three-dimensionally arrayed substrates, it is necessary to provide light receiving elements and light emitting elements on both sides of the substrate or to bore through-holes in the substrate for forming light transmission paths. The process for achieving this is highly complex and is not suited to practical application. As a possible solution to this problem, there is also known an example of effecting light transmission by penetration through the substrate. For example, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 25, No. 1, FEBRUARY 1990 discloses signal transmission between three-dimensional memories by light coupling at an ordinary wavelength. However, since light transmitted through the substrate is not used with this technique, it is necessary to reduce the thickness of the silicon layer by polishing or like processing operations to an order of 0.5 .mu.m to diminish light losses during penetration of light signals through the silicon substrate.